Technical Field
The present invention relates to an electric rotating machine that has a stator and rotors.
Related Art
Techniques relating to motors for hybrid electric vehicles (HEVs) are known. Such a motor for an HEV is a high output motor which is called an interior permanent magnet (IPM) motor. Such an IPM motor makes use of magnet torque and reluctance torque. However, the permanent magnets exerting magnet torque require extra supply of armature current in a reverse magnetic field direction for weak magnetic field, with the increase of induced electromotive force in high-speed rotation. This raises a problem of increasing current loss or causing drag loss due to magnetic attractive force in an unloaded state.
When electromagnets are applied instead of the permanent magnets, a variable field can be created and thus the above problem can be solved. In the application of the electromagnets, current may be supplied by providing a configuration including a brush and a slip ring. However, this raises a problem of impairing reliability and increasing an entire dimension and cost due to addition of a large number of components. Variable magnetic field may be generated in the form of an induction machine or a switched reluctance motor without using a brush. However, this raises a problem of damaging a bearing, providing insufficient endurance against centrifugal force, or causing noise and vibration, due to heat generation of the rotor accompanying the current supply. For this reason, a simple electric rotating machine is desired to be provided, which variably generates a magnetic field with a brushless structure, serves as a generator and a motor, prevents heat generation by a rotor, and has endurance against centrifugal force.
For example, Japanese Patent Application Laid-Open Publication No. 2013-236418 discloses an example of a technique related to an electric rotating machine. This electric rotating machine aims to reduce deformation of the bridges while securing the length of each bridge in a rotor. According to this electric rotating machine, an outer circumferential side portion and an inner circumferential side portion forming each gap in a rotor core are connected by a pair of bridges, with a permanent magnet being inserted into the gap.
However, if the technique disclosed in Japanese Patent Application Laid-Open Publication No. 2013-236418 is applied, permanent magnets are still required to be used. Accordingly, extra armature current is required to be supplied, again raising a problem of increasing current loss or causing drag loss due to magnetic attractive force in an unloaded state.